1. Field of the Invention
The present invention relates to an optically active metal complex catalyst compound showing excellent stereoselectivity as it has in its molecule two moieties i.e. a Lewis acid moiety for activating an electrophile and a Lewis base moiety for fixing the position of a nucleophile, an asymmetric ligand compound constituting said catalyst compound, and a method for producing an optically active cyanohydrin compound employing said catalyst compound.
2. Discussion of Background
Optically active substances have been used in many products or intermediates for agricultural chemicals, pharmaceuticals, etc., and the demand for synthesis for optically active substances at an industrially practical level has been increasing year after year.
For the preparation of an optically active substance by an asymmetric reaction, a catalytic asymmetric synthesis is most efficient and industrially superior, whereby a large amount of an optically active substance can be obtained by using a small amount of an asymmetric source.
As such a catalytic asymmetric synthesis, a method has been known wherein a complex having a rare earth element or a Group 13 element (Al or Ga) as the central metal and further containing an alkali metal and a binaphthol as an asymmetric ligand, is used as a catalyst, whereby it has been successful to efficiently synthesize various optically active substances.
It is believed that such a complex exhibits high stereoselectivity, as the central metal serves as a Lewis acid to activate an electrophile, and the alkali metal binaphthoxide moiety serves as a Br.o slashed.nsted base to fix the position of the nucleophile.
Namely, the above complex makes such excellent stereoselectivity possible as it has, in its molecule, two moieties i.e. the Lewis acid moiety for activating the electrophile and the Br.o slashed.nsted base moiety for fixing the position of the nucleophile. However, with respect to an optical active metal complex catalyst having in its molecules two moieties i.e. a Lewis acid moiety for activating the electrophile and a Lewis base moiety for fixing the position of the nucleophile, there has been no report on a product having a high applicability.
On the other hand, with respect to an optically active cyanohydrin compound, many chemical and enzymatic syntheses have been reported, but little has been known with respect to one which is commonly applicable to any type of a substrate to be used.
Especially, nothing has been reported on an efficient asymmetric catalyst containing an aliphatic aldehyde or an aromatic aldehyde as the substrate.